1. Field of the Invention
This invention is generally directed to methods for securing impact or cutting heads to the shanks of drill bits and especially drill bits for use in down-the-hole mining or drilling operations and more specifically to techniques for joining the component parts by utilizing inertia welding techniques. The invention is further directed to providing a method for enabling drill bit shanks to be recycled by enabling drilling bit heads to be removed from the existing shanks and thereafter replaced by new impact or cutting heads thereby achieving a significant savings in tool costs. The invention further discloses a number of innerface configurations for the components being welded together wherein the interface is defined by generally planar and abutting surfaces having areas defined therein in which flash material may be received as the components are diffusion bonded by inertia welding. Utilizing the teachings of the present invention, it is possible to construct or reconstruct mining bits so that the impact end thereof may be constructed of a very wear resistant material with the shank portion being constructed of a less costly impact resistant steel which can be reutilized after the working end of the bit has become worn.
2. History of the Related Art
In down-the-hole mining operations, use is made of impacting drill bits which consist of an elongated shank having a cutting or impacting head disposed at one end thereof. During the use of such bits, the shanks are impacted and rotated so as to drive the cutting or impacting ends or heads downwardly through subsurface rock or other material formations. Due to the amount of wear and compression that such tools encounter, it is necessary that the cutting or impacting heads be formed of wear resistant alloy materials and include tooth-like components which are manufactured of extremely wear resistant alloy materials. Even when utilizing such wear resistant materials, after periods of time, the cutting or impacting elements must be replaced. In conventional drill bits, the shanks and the cutting or impacting ends were considered to be an integral unit which meant that any time part of the wear resisting materials forming the working end of the tool became worn, the entire drill bit was replaced. Due to the cost of the wear resistant materials which are associated with such drill bits, such a practice is not economically sound.
It is frequently the case that although the working end of the drill bit may become worn, the shank remains in effective working condition. In order to overcome the shortcomings of prior conventional drill bits, it has been proposed to make the work engaging ends or impacting ends of the drill bits selectively mounted to one end of the shanks. In this manner, the cutting ends may be selectively engaged and dismounted after the wear elements associated therewith fail due to prolonged usage.
In U.S. Pat. No. 4,083,415 to Kita et al., one type of mounting mechanism for a replaceable work engaging member for a drill bit is disclosed. In this arrangement, the lower end of the shank includes a reduced diameter portion which extends outwardly from a radial flange provided along the length of the shank. A recessed groove is formed in the reduced diameter portion of the shank and serves as a seat for engagement with ball elements which are secured in place by set screws. The work engaging end portion of the bits are designed to fit over the reduced diameter portion of the shaft of the drill bit and thereafter are locked into engagement with the recessed portions provided therein. By adjusting the set screws, the amount of tension on the ball elements can be regulated so as to permit the work engaging member to be removed as desired.
Unfortunately, such mechanical locking arrangements have not proven to be entirely successful in use in the field. The amount of strain and stress that is placed between the two engaging parts is so great that oftentimes the mechanical locking engagement will fail thereby resulting in the complete loss of the cutting element in the down-hole drilling operation. In addition, the mounting portions of the shafts of the drill bits often become damaged due to the stresses created between the two parts especially when stresses cannot be appropriately counteracted by the mechanical locking elements therebetween. Further, such mechanical locking features require additional bit structure which adds significantly to the increased cost of the drill bits. Another type of mechanical locking arrangement for replaceable head portions for drill bits is disclosed in U.S. Pat. No. Re. 30,952 to White wherein the removable head portion is retained on the shaft portion of the bit by a spline and thread locknut arrangement. Again, such a connection has not proven to be totally successful due to the extreme amount of stress which is imparted between the mechanical locking elements resulting in the failure of the locking components after prolonged use.
In order to avoid the problems associated with mechanical locking arrangements for use with replaceable heads for drill bits, it has been proposed to weld cutting heads to the prepared ends of drill bit shanks. Although such prior art welding techniques do allow the cutting heads to be formed of a more wear resistant or abrasion resistant material while the shank is formed of an impact resistant material, problems remain with failures of the welds during the use of the drill bits. Additional welding techniques utilized to attach the working components of a drill bit to the shank are arc welding techniques which frequently result in an uneven bond between the elements which may result from the weld joint being unevenly heated or from coarse grain structures which are encountered in the weld zone when the liquid metals forming the weld are improperly cooled after they have been heated. Some examples of prior art drilling elements wherein the operating end of the drill is welded by traditional arc welding techniques are disclosed in U.S. Pat. Nos. 1,826,085 to Mulock, 2,096,132 to Pearce, 2,119,349 to Pearce, 2,719,026 to Boice, 4,006,788 to Garner and 4,299,297 to Lloyd. In addition, in U.S. Pat. No. 2,750,156 to Coats, a technique for brazing the cutting elements or heads of drill bits to the shanks is disclosed.